Add TBB threading support.

There are platforms where OpenMP is not available. This
patch adds support for Intel Threading Building Blocks (TBB)
as an alternative threading backend.

Change-Id: I94497d7cba0c3cfaccfc992169236f17fe948ae9

internal/ceres/scoped_thread_token.h

@@ -0,0 +1,61 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2017 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: yp@photonscore.de (Yury Prokazov)
+
+#ifndef CERES_INTERNAL_SCOPED_THREAD_TOKEN_H_
+#define CERES_INTERNAL_SCOPED_THREAD_TOKEN_H_
+
+#include "ceres/thread_token_provider.h"
+
+namespace ceres {
+namespace internal {
+
+// Helper class for ThreadTokenProvider. This object acquires a token in its
+// constructor and puts that token back with destruction.
+class ScopedThreadToken {
+ public:
+  ScopedThreadToken(ThreadTokenProvider* provider)
+      : provider_(provider), token_(provider->Acquire()) {}
+
+  ~ScopedThreadToken() { provider_->Release(token_); }
+
+  int token() const { return token_; }
+
+ private:
+  ThreadTokenProvider* provider_;
+  int token_;
+
+  ScopedThreadToken(ScopedThreadToken&);
+  ScopedThreadToken& operator=(ScopedThreadToken&);
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_SCOPED_THREAD_TOKEN_H_